1. Technical Field
The present invention relates to battery devices, and more particularly to composite structures for batteries which improve capacity and performance.
2. Description of the Related Art
Exponential growth in portable electronic devices such as cellular phones and laptop computers during the past decade has created enormous interest in compact, light-weight batteries offering high energy densities. Growing environmental concerns are driving the development of advanced batteries for electric vehicles and devices. Lithium-ion batteries provide higher energy density compared with other rechargeable battery systems such as lead-acid, nickel-cadmium and nickel-metal hydride batteries. Commercial lithium-ion (Li-ion) batteries use graphite as an anode. Graphite displays a maximum capacity of C=372 mAh/g. Other materials such as carbon nanotubes, Ge nanowires, coaxial MnO/carbon nanotube arrays, etc. may also be employed.
Silicon as an anode for Li-ion batteries has the highest capacity of C=4212 mAh/g. One problem associated with silicon usage is that the silicon volume increases by 400% after Li+ insertion. The volume increase results in silicon pulverization and hence loss in the electrical contact between the active material and the current collector. Therefore, silicon electrodes lead to batteries with high capacity in initial charging/discharging cycles and then the capacity decreases, and the battery exhibits low lifetime.